In waveguide parts used in microwave or millimeter-wave radars and communication devices and antennas having a waveguide structure, a configuration such that complicated hollow conduits are stacked has been desired. Particularly, in a case of consumer products such as an in-vehicle radar, downsizing and high productivity are required. Therefore, as a mode of a conduit part having a hollow waveguide (a conduit) formed therein, a complicated conduit structure can be realized by staking a plurality of plate-like parts having core holes in various shapes formed therein and integrating these parts by surface bonding or the like, and a configuration in which a fastening target part such as a control board is fastened to the conduit part by a screw is used.
As for a method for fastening a screw to the conduit part, there can be considered a method in which a screw hole is formed by machining after conduit parts are integrated, and a method in which conduit parts are integrated after a screw hole is drilled in one conduit part beforehand.
Meanwhile, as a method for fastening a screw to stacked thin plates, for example, a method described in Patent Document 1 has been proposed conventionally. In this proposed method, a dish-shaped reduced part having a fastening hole for a tapping screw is formed on one thin plate, and a supporting unit that supports the dish-shaped reduced part from inside is provided on the other thin plate. The thickness of a fastening part is substantially increased by the dish-shaped reduced part and the supporting unit, and an axial force generated by a fastening torque is supported from inside of the dish-shaped reduced part by the supporting unit to prevent the dish-shaped reduced part from being buckled.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-23944.